Injections of various substances into avian eggs have been employed to decrease post-hatch mortality rates, increase the potential growth rates or eventual size of the resulting chicken, and even to influence the gender determination of the embryo. Similarly, injections of antigens into live eggs have been employed to incubate various substances used in the production of vaccines that have human or animal medicinal or diagnostic applications. Examples of substances that have been proposed as viable treatment (or harvestable vaccine material) alternatives for delivery via in ovo injection of avian embryos include live culture vaccines, antibiotics, vitamins, and even competitive exclusion media (a live replicating organism). Specific examples of treatment substances are described in U.S. Pat. No. 4,458,630 to Sharma et al, and U.S. Pat. No. 5,028,421 to Fredericksen et al.
Conventionally, the physical injection has been typically targeted at preferred positions within the egg to administer the substance into specific developing regions of the embryo. As understood by those of skill in the art, as the incubation period progresses towards maturity and hatching, the embryo and its membranes, the air cell, the allantois, and yolk sac correspondingly change in volume and position within the egg shell. Additionally, the quantitative volume of the enclosed fluids can vary. For example, the density of the allantois varies over the incubation period. Thus, selection of the site and time of treatment can impact the effectiveness of the injected substance as well as the mortality rate of the treated embryos. See e.g., U.S. Pat. No. 4,458,630 to Sharma et al., U.S. Pat. No. 4,681,063 to Hebrank, and U.S. Pat. No. 5,158,038 to Sheeks et al.
Current injection methods that rely on substance delivery using a cannulated needle, however, present the risk of introducing infection into the target egg and/or injuring the injected embryo. There is still a need, therefore, for injection methods and apparatus that can deliver treatment substances to avian embryos but which do not, after piercing the outer hard shell, mechanically penetrate into the egg contents or the embryo. There is also a need for multisite injection methods and apparatus that will have a reduced likelihood of infecting the target egg due to mechanical penetration into the egg contents. There is a further need for automatic injection methods for treating multiple eggs simultaneously or in rapid and continuous succession without mechanically penetrating into the egg interior.